I might be way off, but there seems to be part of a head (with one small dark eye showing) and jaw of a creature in the top left hand corner. Could it be a caddis larva, that is only partly covered with debris, that they use to camouflage themselves?

What could be the abdomen doesn't look quite right though - unless its from underneath maybe.

Given the uniformity of the placement of the structures within the it, it could be an egg mass. Having done a google search of egg masses I came up with this of egg masses of the Chironomidae family of non-biting midges, there is more info and images here if you scroll down, looks pretty similar to me!